Inter‐ and intrarater reliability of four single‐legged hop tests and isokinetic muscle torque measurements in children

Purpose Single‐legged hop tests and isokinetic muscle torque are common outcome measures in the evaluation of knee function. The reliability of the single‐legged hop tests in children has not been documented. The aim was to examine inter‐ and intrarater reliability of four single‐legged hop tests and isokinetic muscle torque measurements in children. Methods Twenty‐eight sports‐active children (12.4 ± 0.3 years old) were tested three times in two test sessions separated by 1 week. They performed four single‐legged hop tests and concentric isokinetic torque measurements during knee extension and flexion. Inter‐ and intrarater reliability were calculated using the intraclass correlation coefficient (ICC 2,1). Relative terms of the standard error of measurement (SEM %) and smallest real difference (SRD %) were emphasized to allow comparison between the different variables. Results Twenty‐six children were included for statistical analysis. ICCs for inter‐ and intrarater reliability were moderate to high for the hop tests (0.62–0.91) and isokinetic measurements (0.76–0.87). SEMs % were low for the hop tests (3.9–7.4 %) and the isokinetic measurements (5.2–8.9 %). SRDs % were 20.5 % or less for the hop tests, 15.7 % or less for knee extension, and 24.6 % or less for knee flexion. Conclusion The single‐legged hop tests and isokinetic muscle torque measurements demonstrated moderate‐to‐high reliability with low measurement error in sports‐active children. A change above 20.5 % for the single‐legged hop tests, 15.7 % for knee extension, and 24.6 % for knee flexion is necessary to represent a real change in knee function. Level of evidence III.